Service of the Engine is a common local Chichewa-English expression in the Malawian fishing village where the author did her fieldwork. It refers to the practice of taking various pills--known locally as Ciba--in order to prevent and cure diseases associated with sex. This study explores the sensitive interface between the use of pharmaceuticals, available through an extensive informal distribution system, and self-treatment of sex-related diseases. The author examines morally sensitive situations in which men and women opt for Ciba, and evaluates (...) its efficacy, or effectiveness. The discussion not only covers physical and metaphorical aspects of efficacy, but also the possible social and moral effects of medication. It offers a fresh and empirically grounded perspective on the links between efficacy, sex-related diseases and moralities. Birgitte Bruun graduated from the Institute of Anthropology, University of Copenhagen, Denmark and is currently working with reproductive health projects for United Nations Population Fund in Jakarta, Indonesia. (shrink)